The present invention relates to light strings such as those used for holiday lighting and, more particularly, to shunts in the sockets of the lights in the string.
Strings of lights are typically wired electrically in series. Consequently, when one light in the string burns out or is removed, all the lights in the string go out. Determining which light needs to be replaced is tedious. If the string has 50 or more lights and the string is attached to a Christmas tree, finding the burned out or missing bulb can be very tedious.
For a number of years, this problem has been solved, or at least avoided, by the use of shunts that allow current to pass directly between the terminals of the defective lamp, bypassing the missing or defective bulb filament. Passing electrical current from one lamp to the next regardless of the condition of the bulb in any individual lamp allows the remaining lamps to continue to operate.
Shunts are typically found in two places in prior art lamps, namely, in the glass bulb and in the socket. The shunts inside the glass bulb are typically coils of wire wrapped around the conductive elements (called Dumet wires). When the filament fails, the oxide coating on the coils of wire that theretofore prevented direct conduction of electricity is burned off and the coil welds itself to the Dumet wires, thereby providing a new electrically conductive path for passing the electrical current.
Of the type of shunt that is located in the socket, there are two types, namely, solid state shunts and mechanical shunts. Among the mechanical shunts, for example, there is a set of spring contact terminals that is the subject of U.S. Pat. No. 6,257,740. These spring contacts are pushed apart when the bulb holder is inserted into the socket and spring back together when the bulb holder is removed, thereby allowing the current to pass from one terminal to the other directly. This type is strictly for use when the bulb (and its bulb holder) is removed and does not address the issue of a burned out bulb. This type of shunt works well and has enjoyed commercial success.
Another mechanical shunt is disclosed in U.S. Pat. No. 7,253,556, which is invented by the present inventor and is commonly owned by applicant. This mechanical shunt is a nearly horizontal flat strip of metal held in place between the two electrical terminals in a light socket by a shunt holder. The ends of the shunt extend laterally and slightly downwardly to engage the electrical terminals on the socket wall. When the bulb holder, which is hollow, is inserted into the socket, the shunt holder together with the shunt is received inside the hollow bulb holder, and, as the shunt enters the bulb holder, its ends are bent down and away from the electrical terminals, thereby allowing electrical current to pass to and through the Dumet wires and thence to the filament in the bulb rather than directly through the shunt.
Note with respect to both of the mechanical shunts just described, that a special structural feature of the bulb holder portion of the lamps interacts with the shunt. While forming all the bulb holders of a given string of lights with the structural feature is not a problem, it can present a problem when the user either needs to replace a lamp having the special structural feature with an ordinary lamp or desires to replace the lamp with a lighted ornament. There are, for example, so-called pigtail ornaments, such as that described in U.S. Pat. No. 6,764,205, issued to Peloquin. This type of ornament contains a light or other electrical load (e.g., sound emitting device or motor) that is connected to a cord (or “pigtail”), the distal end of which has a plug that is inserted into a socket of a light string to power the ornament. The plug of the ornament is typically shaped much like a bulb holder. Because the connector on the end of the pigtail does not have the special structure needed to activate the mechanical shunt, these types of ornaments are operated without the shunt protection or cannot be operated because the shunt is never deactivated and the ornament is not energized. This presents a convenience issue to the user.
There are a huge number of light strings manufactured and sold each year throughout the world. The number is so large that even small changes that, for example, reduce material requirements, simplify manufacturing, or improve safety, reliability, or compatibility make a huge difference in the costs to manufacture. Accordingly, there remains a need for a better mechanical shunt for use in the sockets of the lamps of light strings.